TDBM: A DBM Library with Atomic Transactions

The dbm database library introduced disk-based extensible hashing to UNIX. The library consists of functions to use a simple database consisting of key/value pairs. A number of work-alikes have been developed, offering additional features and free source code. Recently, a new package was developed that also offers improved performance. None of these implementations, however, provide fault-tolerant behaviour.

In many applications, a single high-level operation may cause many database items to be updated, created, or deleted. If the application crashes while processing the operation, the database could be left in an inconsistent state. Current versions of dbm do not handle this problem. Existing dbm implementations do not support concurrent access, even though the use of lightweight processes in a UNIX environment is growing. To address these deficiencies, tdbm was developed. Tdbm is a transaction processing database with a dbm-like interface. It provides nested atomic transactions, volatile and persistent databases, and support for very large objects and distributed operation.

This paper describes the design and implementation of tdbm and examines its performance.